YikStik3

Motivation

This is a "replacement" for Bdale's first L3 certification airframe, YikStik, which was mostly lost... and a follow-on to 2YikStik, which had one and only one "way too exciting" flight at LDRS 30. We recovered the nose cone, tail cone, rail buttons, and all of the electronics from 2YikStik. Everything else is new for this build.

Robert is very interested in measuring the temperature of a nose cone and a fin on a rocket at speeds above Mach. This led Bdale to design a TeleMetrum companion board called TeleScience capable of hosting up to 12 NTC thermistors for temperature data collection. As was the case with 2YikStik, the plan is to fly two TeleMetrum+TeleScience setups, one mounted in the nose cone and one mounted in the fin can. The one in the fin can will be responsible for apogee deployment, and the one in the nose cone will handle main deployment.

We will again fly a custom 98mm nose cone with the temperature sensors embedded in the glass layers made for us by Jeff Lane of Shock Wave Rocketry.

Design Details

• 98mm Performance Rocketry G-10 convolute glass air frame
• 98mm Performance Rocketry G-12 filament-wound glass couplers
• 75mm PML phenolic motor mount
• Shock Wave Rocketry fiberglass 98mm Von Karman 6:1 nose cone
• custom fins, using 3/16 inch birch plywood laminated with carbon fiber and a fibreglass sanding veil
• 3/8 inch birch plywood centering rings and bulkheads, CNC milled, the two that hold the fins are double thickness (3/4 inch) and notched for perfect fin alignment.

The OpenRocket design file is YikStik3.ork.

Thermistors

The temperature sensors chosen are 0.8 mm diameter glass bead NTC thermistors made by EPCOS, model B57540G0303F000. These were chosen because of their small size, and turn out to have a very fast response time to changing temperatures.

The leads were extended with 30 gauge wire wrap wire using twisted pairs of black plus a color. The colored lead was insulated from the bead back over the solder joint using 1/16 inch heat shrink tubing. The epoxy used for the nose cone and fin was tested and confirmed to have essentially no conductivity.

Electronics

The airframe geometry led us to decide to build two electronics bays, one in the airframe immediately aft of the nose cone, and the other in the fin can.
Each bay holds a production TeleMetrum, a prototype companion board called TeleScience, a 1000 mAh LiPo battery, and a power switch.

The prototype TeleScience boards support connection of up to 12 NTC thermistors along with other capabilities.

Installing the electronics in the fin can bay was a huge challenge due to the restricted space between the MMT and airframe. All of the through-hole connectors on both boards were removed, along with the GPS antenna and beeper on the TeleMetrum board, yielding two boards with no parts on the "top" side. A short piece of ribbon cable was hard-wired between the companion ports on the two boards, and the LiPo battery leads were soldered to TeleMetrum. The TeleMetrum board was equipped with an edge-launched SMC RF connector (smaller in diameter than an SMA) for attachment to an off-board antenna. Then the boards were installed on minimum-height standoffs above the phenolic motor mount behind a hatch cut in the airframe between two fins, with the GPS antenna and beeper epoxied down to the side of the TeleMetrum board. The battery was mounted as far forward as possible and blocked in with some small bits of scrap balsa stuck down with super glue. The power switch was mounted near the aft end of the bay such that a small screwdriver reaching through the 0.25 inch static vent can be used to turn things on and off.

Fintenna

On 2YikStik, one of the big disappointments was a very poor signal from the UHF transmitter on the TeleMetrum board mounted in the fin can. This isn't surprising, since the antenna was just a wire whip running in parallel with and very close to the motor casing. For this build, I decided to try something completely different.

The quick summary is that I'm loading up the two fins that don't have thermistors in them as an antenna. And it works brilliantly!

Before bagging the fins with the CF and glass lamination, I put 1 inch wide copper foil tape on two of the fin substrates, running from near the tip down to the root. Then the fins were bagged with 2 layers of 5.7 oz 2x2 twill carbon fiber and a 6 oz glass sanding veil layer on both sides, all in one bagging operation to ensure all the layers formed a strong chemical epoxy bond.

After unbagging, while the epoxy was still somewhat leathery, I carefully cut the CF back at the root edge of each fin exposing the copper foil. The fins were then allowed to cure and get sanded normally. When installing them in the airframe, I oriented them so that the thermistor fin is on the anti-rail side of the airframe, and the two copper-foil-equipped fins bracket the rail side, with the copper foil sides facing each other across the rail-side valley.

After applying fin to fin glass across the motor mount, additional copper foil tape was used to join the two fins, soldering the new foil to the foil embedded in the fins. I then cut a "gap" in the center of the space between the two fins, and installed a 1.5-20pF piston trimmer capacitor with the screw aimed aft, and a piece of small diameter teflon coax with two ferrite beads on the forward side of the gap. The coax was run through a hole near the root of the fin separating this valley from the ebay and terminated with an SMC connector to mate with the TeleMetrum board.

I'm pleasantly surprised at how well this seems to work. With a Pro75 6xl case installed, the variable cap allows the antenna to be tuned to about 1.3:1 SWR, and the resulting transmitted signal seems strong...

Build

Parts gathered during late 2011 and early 2012. Built starting in early March of 2012, and completed in time for NCR's Mile High Mayhem 2012.

The nose cone was custom fabricated by Jeff Lane at Shockwave Rocketry, with thermistors embedded.

The fins are 3/16 inch birch ply, tapered on the leading and trailing edges, then covered with two layers of 5.7 oz 2x2 twill carbon fiber and a layer of 6 oz glass as a sanding veil, all vacuum bagged with West Systems laminating epoxy using a kitchen food saver appliance. The two CF layers are rotated 45 degrees from each other.

We're moving from the Giant Leap Rocketry 98mm Magnaframe-based Dynawind to G-10 glass tubing this time around. Dynawind is lighter and strong enough, but we want to use glass couplers this time around for more strength, and that leads to fit issues with the Magnaframe-based Dynawind tubing. So even though it's slightly heavier, we're going with an all-glass build this time. We'll lose a little bit of max velocity, but hopefully it'll all hang together!

The tailcone is a no-longer-available Giant Leap 98-75mm Slimline tailcone recovered from 2YikStik's wreckage.

All rings and bulkheads were cut using a CNC milling machine from 3/8 inch birch plywood. The fin forward and leading edge rings are made from 3/4 inch thick birch plywood, mostly to provide sufficient depth for milled fin slots.

Photos

I've put all the build photos I took together in one place.

Friends who were present for YikStik3's first flight during the Kloudbusters Airfest 18 launch over Labor Day weekend 2012 took these photos and videos:

• Terry Lee
• Tom Marble

Flights

The intended first flight of YikStik3 was to be at NCR's Mile High Mayhem 2012 on an unreleased Cesaroni Pro75 6xl Imax reload. Unfortunately, the jet stream was parked over the site yielding strong upper level winds, such that it would not have been possible to keep the airframe inside the waiver cylinder during recovery... so we didn't fly.

The motor was certified in early August as the Pro75-6GXL 9977-M2245-IM-P.

I was able to fly YikStik3 for the first time at the Kloudbusters Airfest 18. They've got a huge waiver cylinder and an awe-inspiring recovery area .. which it turns out we didn't need much of! The airframe achieved approximately Mach 2.2 and 21,660 feet above ground. More details will be posted once we have time to analyze the data we collected.

This airframe, along with many other things, was lost in the Black Forest Fire.